Dust-driven Dynamos in Accretion Disks

Magnetically driven astrophysical jets are related to accretion and involve toroidal magnetic field pressure inflating poloidal magnetic field flux surfaces. Examination of particle motion in combined gravitational and magnetic fields shows that these astrophysical jet toroidal and poloidal magnetic fields can be powered by the gravitational energy liberated by accreting dust grains that have become positively charged by emitting photo-electrons. Because a dust grain experiences magnetic forces after becoming charged, but not before, charging can cause irreversible trapping of the grain so dust accretion is a consequence of charging. Furthermore, charging causes canonical angular momentum to replace mechanical angular momentum as the relevant constant of the motion. The resulting effective potential has three distinct classes of accreting particles distinguished by canonical angular momentum, namely (i) "cyclotron-orbit", (ii) "Speiser-orbit", and (iii) "zero canonical angular momentum" particles. Electrons and ions are of class (i) but depending on mass and initial orbit inclination, dust grains can be of any class. Light-weight dust grains develop class (i) orbits such that the grains are confined to nested poloidal flux surfaces, whereas grains with a critical weight such that they experience comparable gravitational and magnetic forces can develop class (ii) or class (iii) orbits, respectively producing poloidal and toroidal field dynamos.Comment: 70 pages, 16 figure

Advancing Precambrian palaeomagnetism with the PALEOMAGIA and PINT(_QPI) databases.

State-of-the-art measurements of the direction and intensity of Earth's ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries

Analysis of output surface damage resulting from single 351 nm, 3 ns pulses on sub-nanosecond laser conditioned KD2PO4 crystals

We observe that by conditioning DKDP using 500 ps laser pulses, the bulk damage threshold becomes essentially equivalent to the surface damage threshold. We report here the findings of our study of laser initiated output surface damage on 500 ps laser conditioned DKDP for test pulses at 351 nm, 3 ns. The relation between surface damage density and damaging fluence (r(f)) is presented for the first time and the morphologies of the surface sites are discussed. The results of this study suggest a surface conditioning effect resulting from exposure to 500 ps laser pulses

Differential Impacts of Online Delivery Methods on Student Learning: A Case Study in Biorenewables

In 2007, a Virtual Education Center for Biorenewable Resources was initiated that offered three distance education courses, one being Biorenewable Resources and Technology (BRT) 501 – Fundamentals of Biorenewable Resources and Technology, the subject of this study. The primary objective was to determine if course delivery method (video lecture format and the other in menu-driven auto-tutorial presentations (MDAP) deliv¬ered via Flash format), student major (agricultural and non-agricultural), and gender influence online student learning in BRT 501. We found that BRT 501 student performance was not significantly impacted by module delivery method. Students with agricultural majors were outperformed by students with non-agricultural majors, most of whom were engineering students, on the midterm and final exams, and course grade. Gender dif¬ferences seen on the biomass-module first-attempt total quiz score disappeared for the final total quiz score on that module

Comparison between S/1 and R/1 tests and damage density vs. fluence (rho(phi)) results for unconditioned and sub-nanosecond laser-conditioned KD2PO4 crystals

We present S/1 and R/1 test results on unconditioned and 355 nm (3{omega}), 500 ps laser conditioned DKDP. We find up to {approx}2.5X improvement in fluence in the S/1 performance after 3{omega}, 500 ps conditioning to 5 J/cm{sup 2}. For the first time, we observe a shift to higher fluences in the R/1 results for DKDP at 3{omega}, 7 ns due to 500 ps laser conditioning. The S/1 results are compared to {rho}({phi}) results previously measured on the same DKDP crystal [1]. A consistent behavior in fluence was found between the S/1 and {rho}({phi}) results for unconditioned and 500 ps conditioned DKDP. We were successful at using Poisson statistics to derive a connection between the S/1 and {rho}({phi}) results that could be tested with our data sets by trying to predict the shape of the {rho}({phi}) curve. The value for the power dependence on fluence of {rho}({phi}) derived from the S/1 data was {approx}11 {+-} 50%. The results presented and discussed here imply a strong correlation between the damage probability (S/1) test and {rho}({phi}). We find a consistent description of the two test types in terms of a power law {rho}({phi}) and that this basic shape held for all cases, i.e. the shape was invariant between unconditioned and conditioned results